Amorphous Ni-based Cr- and P-bearing alloys have long been recognized as having enormous commercial potential because of their high corrosion resistance. (Guillinger, U.S. Pat. No. 4,892,628, 1990, the disclosure of which is incorporated herein by reference.) However, the viability of these materials has been limited because conventional Ni-based Cr- and P-bearing systems are typically only capable of forming foil-shaped amorphous articles, having thicknesses on the order of several micrometers (typically below 100 micrometers).
The thickness limitation in conventional Ni-based Cr- and P-bearing alloys is attributed to compositions that require rapid solidification (cooling rates typically on the order of hundreds of thousands of degrees per second) to form an amorphous phase. For example, Japanese Patent JP63-79931 (the disclosure of which is incorporated herein by reference) is broadly directed to Ni—Cr—Nb—P—B—Si corrosion-resistant amorphous alloys. However, the reference only discloses the formation of foils processed by rapid solidification, and does not describe how one would arrive at specific compositions requiring low cooling rates to form glass such that they are capable of forming bulk centimeter-thick glasses, nor does it propose that the formation of such bulk glasses is even possible. Likewise, United States Patent Application US2009/0110955A1 (the disclosure of which is incorporated herein by reference) is also directed broadly to amorphous Ni—Cr—Nb—P—B—Si alloys, but teaches the formation of these alloys into brazing foils processed by rapid solidification. Finally, Japanese Patent JP2001-049407A (the disclosure of which is incorporated herein by reference) does describe the formation of Ni—Cr—Nb—P—B bulk amorphous articles, but falsely advises the addition of Mo to achieve bulk-glass formation. Only two exemplary alloys capable of forming bulk amorphous articles are presented in this prior art, both containing Mo, and the bulk amorphous articles formed by the exemplary alloys are rods with diameters of at most 1 mm. Another two exemplary Ni—Cr—Nb—P—B alloys capable of forming glassy rods 1-mm in diameter are also presented in an article by Hashimoto and coworkers (H. Habazaki, H. Ukai, K. izumiya, K. Hashimoto, Materials Science and Engineering A318, 77-86 (2001), the disclosure of which is incorporated herein by reference).
The engineering applicability of these two-dimensional foil-shaped articles is very limited; applications are typically limited to coating and brazing. The engineering applicability of 1-mm rods is also restricted to very thin engineering components having sub-millimeter thickness. For broad engineering applicability, “bulk” three-dimensional articles with dimensions on the order of several millimeters are typically sought. Specifically, slab-shaped articles 1 mm in thickness, or equivalently (from a cooling rate consideration) rod-shaped articles 3 mm in diameter, are generally regarded as the lower limits in size for broad engineering applicability. Another requirement for broad engineering applicability is the ability of millimeter-thick articles to undergo macroscopic plastic bending under load without fracturing catastrophically. This requires that the bulk metallic glasses have relatively high fracture toughness. Accordingly, a need exists for Ni-rich Cr- and P-bearing alloys capable of forming bulk glasses.